Electrically Eraseable Programmable Read Only Memory

• Serial
  • Microchip
    • 24AA256 - 32kx8 Serial I2C EEPROM  
    • 24C64
    • 24C65
    • 24C32A driver for 16c74a from Virgil Stamps 
    • 24LC16B see: http://www.shm.monash.edu.au/~r.kreymborg/code.html (cached 20000110) actually a RAM
    • 24LC08 see:I2CROM.asp in the UMPS evaluation version from http://www.vmdesign.com
  • Microchip 93CX6 Serial MicroWire 128-1kbyte EEPROMs
    • Interfacing 93CX6 EEPROMs to PIC16C5X Microcontrollers
  • Microchip Questions and Answers Concerning Serial EEPROMs
  • Xicor X25256 5Mhz SPI clock 32KBx8 8-pin SOIC 100,000 write cycles typical 10 msec write cycle 64-byte page mode writes ad says $3.15/1000
• Parallel
  • Microchip 28C16A 2Kx8 Parallel Electrically Erasable PROM
  • Microchip 28C64A 8Kx8 Parallel Electrically Erasable PROM

Avoiding EEPROM corruption

Serial EEPROM Solutions vs. Parallel Solutions - The cost break even point for serial I2C non-volitile memory from useing multiple 32kx8 EEPROMs to using parallel flash memory with an I2C controller is at about 128k as of late 1999.

Ian Chapman <pic@chapmip.demon.co.uk> says:

BTW, I've just spotted an interesting point in AN709 about I2C EEPROMs which can power up in an incorrect state. The following initialisation sequence after power-up is recommended to resolve this:

• START bit
• Clock in nine bits of '1'
• START bit
• STOP bit

I haven't seen this in any examples of I2C master code before, but AN709 gives a good explanation of why it is needed to avoid the possibility of an erroneous write to the EEPROM.

Extending lifetime and reliability in EEPROMs

FLASH@

See also:

• MicroChip Technologies Memory Devices: Serial-64 to 256k, Parallel EEPROM
• Xicor Serial EEPROMs 8k
• ST Microelectronics Serial EEPROMs 8k
• U24C08 I2C EEPROM Chip Programming
• http://www.asamicros.com/ Serial EEPROM utility and code.

See:

Code:

• Chuck McManis shares this code:

  
   
  This code will write the EEPROM on the 16F628 in chunks.
  
  ;
  ; Written: 14-Apr-2002, Chuck McManis
  ;
  ; Uses the temporary variable EE_LEN, EE_SRC, and EE_DST
  ; During write Source is RAM and Destination is EEPROM
  ;
  ; Note: Due to a bug in the 16F628 you can "overrun" the ability
  ; of the chip to write the EEPROM if you just monitor the WR bit
  ; in EECON1 (if you write immediately after it goes low the EEPROM
  ; may not be written.
  ;
  ; Thus this macro assumes that when it starts there is not a write
  ; currently in progress!
  ;
  ; Usage: EEWRITE <data bytes address (0-0xff)>, <eeprom address>, <len>
  ;
  ; On the 16F628, EE_LEN, EE_SRC, and EE_DST should be in the range
  ; 0x70 - 0x7F (mirrored on all ram banks)
  ;
  ;                                
  EEWRITE MACRO   SRC_ADDR, DST_ADDR, LEN
          LOCAL   WLOOP
         
          MOVLW   LEN             ; Get length
          MOVWF   EE_LEN          ; Store it in count
          MOVLW   SRC_ADDR        ; Get the source address
          MOVWF   EE_SRC          ; Store in the source addr
          MOVLW   DST_ADDR        ; EEPROM Destination address
          MOVWF   EE_DST          ; Store it too
  WLOOP:  
          BCF     PIR1, EEIF      ; Clear this flag...
          MOVF    EE_SRC,W        ; Source Address
          MOVWF   FSR             ; Store in FSR
          MOVF    INDF,W          ; Get a data byte
          BSF     STATUS, RP0     ; Switch to Bank 1
          MOVWF   EEDATA          ; Store the data byte in EE Data
          MOVF    EE_DST,W        ; Get the destination address
          MOVWF   EEADR           ; .. this byte goes here
          BSF     EECON1, WREN    ; Enable Writes to EEPROM
  ;       BTFSS   EECON1, WR      ; This should work but doesn't (see
  ;       GOTO    $-1             ; below) it only writes 2 of n bytes.        
          BCF     INTCON, GIE     ; Interrupts off.
          MOVLW   H'55'           ; Magic Sequence (Sequence Start)
          MOVWF   EECON2          ;       ... 
          MOVLW   H'AA'           ;       ... 
          MOVWF   EECON2          ;       ... 
          BSF     EECON1, WR      ; and Write it! (Sequence End)
          BSF     INTCON, GIE     ; Interrupts are allowed again.
          BCF     EECON1, WREN    ; Disable future writes.
          BCF     STATUS, RP0     ; back to bank 0
          BTFSS   PIR1, EEIF      ; Wait for it to finish, this slows
          GOTO    $-1             ;   ... us down! (bug! see above)
          INCF    EE_SRC, F       ; Add 1 to source and destination
          INCF    EE_DST, F       ;  ... addresses (no overlap)
          DECFSZ  EE_LEN,F        ; Decrement the length and ...
          GOTO    WLOOP           ; ... loop if non-zero.
          ENDM
  

For another example of reading the EEPROM, see PIC 16F876 full initialization sample program /techref/microchip/16f877/snipp.htm .

Questions:

• kavi_k50 at -Remove-hotmail.com asks: " I'm trying to interface an external EEPROM memory to 16f877.
  can anybody help us out...........??" +

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